If you are using single speed motors to drive fans or pumps, you may be able to save energy through the use of a variable frequency drive. The variable frequency drive (VFD) can convert a single speed motor to variable speed with no modification to the motor itself. This can be an efficient way to convert, for example, constant volume air systems into variable volume. VFD's are readily available for motors from 1 hp to 300 hp and are easily installed directly into the power line leading to the motor, replacing the existing motor starter. Incentives are available for the installation of VFD's.
Many fan and pump systems have a cost effective application for variable frequency drives. Quite often these systems have a variable flow rate using throttling devices such as valves and dampers to vary the flow. Throttling devices essentially waste excess energy to maintain a given pressure or flow and the use of a VFD can be very cost effective in these situations. Typical examples of systems using throttling devices are: booster pumps for domestic water, process chilled or condenser water systems and fan discharge dampers.
Other variable flow systems use mechanical or electrical methods such as inlet vanes, outlet dampers, eddy current clutches, hydraulic couplings and variable pitch pulleys to vary the speed of the fan or pump. These are more efficient than throttling devices but not as efficient as VFD's. Some fan and pump systems are currently constant flow but may be converted to variable flow systems by making modifications to the system.
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